怎样恢复一个重定向了的标准流?

如果要将重定向了的标准流恢复到初始状态，可以使用标准C库函数dup()和fdopen()。

dup()函数可以复制一个文件句柄，你可以用dup()函数保存对应于stdout标准流的文件句柄。fdopen()函数可以打开一个已用dup()函数复制了的流。这样，你就可以重定向并恢复标准流，请看下例：

#include <stdio.h>
void main(void);
void main(void)
{
    int orig-stdout;
    /* Duplicate the stdout file handle and store it in orig_stdout.  */
    orig_stdout = dup (fileno (stdout));
    /* This text appears on-screen.  */
    printf("Writing to original stdout... \n") ;
    /* Reopen stdout and redirect it to the "redir. txt" file.  */
    freopen("redir.txt", "w", stdout);
    /* This text appears in the "redir. txt" file.  */
    printf("Writing to redirected stdout.., \n");
    /* Close the redirected stdout.  */
    fclose (stdout);
    /* Restore the original stdout and print to the screen again.  */
    fdopen(orig_stdout, "w" );
    printf("I'm back writing to the original stdout. \n");
}